Betacoronavirus Infection Outbreak, São Paulo, Brazil, Fall 2023

We report a human coronavirus OC43 infection outbreak in hospitalized patients and healthcare workers in São Paulo, Brazil, occurring after SARS-CoV-2 cases disappeared. Infection was associated with healthcare workers in 5 (29.4%) patients. Routine surveillance including a respiratory virus panel can improve coronavirus detection in both healthcare professionals and patients.

Radiologic images were obtained for 14 of 16 inpatients who had HCoV-OC43, and 62.5% (10/16) had an alteration detected by chest computed tomography.Radiologic findings included lung opacities, bilateral interstitial infiltrate, consolidations, and centrilobular micronodules with a unifocal or multifocal ground glass pattern, all of which were predominantly distributed within the lower lobes.
A probable nosocomial acquisition might have occurred because the infection rate among healthcare workers peaked earlier (May) than the observed inpatient peak rate (June) (Table ).Five (31.2%) inpatients who had HCoV-OC43-positive samples were

RESEARCH LETTERS
We report a human coronavirus OC43 infection outbreak in hospitalized patients and healthcare workers in São Paulo, Brazil, occurring after SARS-CoV-2 cases disappeared.Infection was associated with healthcare workers in 5 (29.4%) patients.Routine surveillance including a respiratory virus panel can improve coronavirus detection in both healthcare professionals and patients.housed within different wards several days after admission; thus, it was possible to confirm nosocomial acquisition.In those cases, HCoV-OC43 transmission took place within inpatient wards, specifically during activities involving direct contact with a healthcare worker.Contact tracing connected patient cases to interactions with healthcare workers.
The SARS-CoV-2 positivity rate during the outbreak period (March-June) varied from 7.3% to 27.9% (Figure ); no cases were reported in June.To provide background for the outbreak, we conducted surveillance testing for respiratory viruses collected 2 months before (January-February) and after (July-August) the outbreak; no HCoV was detected during those periods.In previous studies conducted at our hospital before the COVID-19 pandemic, we did not observe >5% monthly circulation of HCoVs during the study years under investigation (5).The HCoV-OC43 outbreak peak occurred after the disappearance of SARS-CoV-2 cases (Figure ).
In this outbreak, hospitalized patients showed evolution of a severe form of infection caused by HCoV-OC43.Nirmatrelvir/ritonavir is a promising antiviral drug combination in preclinical studies that inhibits the proteolytic activity of SARS-CoV-2 M pro , a cysteine protease found in the family Coronaviridae (6), and might be useful for treating HCoV-OC43 infections.
At the end of March 2023 in Brazil, the National Health Surveillance Agency (Agência Nacional de Vigilância Sanitária) updated guidelines for mask use in healthcare settings.Since April 2023, the hospital committee has relaxed the requirement for universal mask use, making them obligatory only in areas designated for patient care (7).Relaxing mask use by healthcare workers who provide care to high-risk patients likely contributed to nosocomial acquisition of HCoV-OC43.Furthermore, healthcare workers who had respiratory infections other than SARS-CoV-2 infections were likely less vigilant in using personal protective equipment during patient care.In addition, an unconscious relaxation in maintaining precautions might have occurred, possibly because persons did not perceive themselves as potential transmitters.
In conclusion, we report the occurrence of HCoV-OC43 causing severe acute respiratory infection that might be underestimated because of a lack of better diagnostic approaches for viral respiratory infections, particularly in high-risk patients.Routine surveillance using a diagnostic panel of respiratory viruses can improve detection in both healthcare workers and patients and can help determine prevalence and prevent transmission of different viruses.
T.S.S.C was supported by the Evandro Chagas Institute at the Ministry of Health of Brazil and the School of Medicine at the Federal University of Pará.N.B., A.H.P., and T.S.S.C. conceived and designed the study and contributed to data analysis; A.H.P., D.B.F., and G.B. contributed to diagnostic, patient, and public health surveillance data analysis; and N.B., T.S.S.C., and G.B. wrote the first draft.All authors contributed and approved the final manuscript.About the Author Dr. Chaves is an infectious and tropical diseases research scientist at the Evandro Chagas Institute/Secretariat of Health and Environment Surveillance at the Brazilian Ministry of Health, professor at the Faculdade de Medicina da Universidade Federal do Pará, Belém, Brazil, and a postdoctoral research scientist at the Federal University of São Paulo, São Paulo, Brazil.Her primary research interests are epidemiologic and clinical studies of infectious and tropical diseases, emerging and reemerging diseases, public health¸ and travel medicine.

Figure .
Figure.Positivity rates for SARS-CoV2 and HCoV in Hospital São Paulo during betacoronavirus infection outbreak, São Paulo, Brazil, March-June 2023.Blue bars indicate the number of samples tested each month.Purple and red lines indicate the percentage of samples that were positive for each virus.HCoV, human coronavirus.

Table .
HCoV-positive case-patients by month, age, and participant groups during the betacoronavirus infection outbreak in Hospital *Values are no.positive/no.tested (%).HCoV, human coronavirus; NA, not applicable.